A modern mobile device can function as a computer and as a cellular telephone. For example, the mobile device can perform traditional computer functions, such as executing application programs, storing various data, and displaying digital images. These functions can be performed in an application subsystem of the mobile device. When the mobile device functions as a cellular telephone, the mobile device can initiate and receive phone calls, identify cellular tower connections, and determine when and whether to switch cellular towers. These functions can be performed in a baseband subsystem of the mobile device. In addition to cellular communication capability, some modern mobile devices include wireless transceivers that allow data to be transmitted and received through access points of a wireless local area network.